Serotonin (5-hydroxytryptamine; hereinafter, also referred to as “5-HT”) is known as one of main neurotransmitters in central nervous system, and it is also known that serotonin is involved in various brain functions such as emotional reaction and cognitive function.
5-HT1A receptor which is one of 5-HT receptor subtypes is a Gi/o protein-coupled receptor, and is expressed in cerebral cortex, hippocampus, raphe nucleus, amygdala, and the like. Compounds having agonist activity for 5-HT1A receptor includes, for example, tandospirone and buspirone. Tandospirone is used as a medicament for treating dysphoria and fear in neurosis, physical symptoms in psychosomatic diseases (autonomic dysregulation, essential hypertension, peptic ulcer), and dysphoria, anxiety, irritation, and sleep disorders. Buspirone is used as a medicament for treating generalized anxiety disorders (Non-Patent Literature 1).
5-HT2A receptor is a Gq/11 protein-coupled receptor, and is highly expressed in cerebral cortex, hippocampus, raphe nucleus, and the like. Drugs having antagonist activity for 5-HT2A receptor include antidepressant drugs, mianserin and mirtazapine. Atypical antipsychotic drugs which also have antagonist activity for 5-HT2A receptor are used as a medicament for treating schizophrenia, bipolar disorders, major depression, autistic spectrum disorder, and the like (Non-Patent Literature 2, Non-Patent Literature 3).
As described above, it is shown that agonists for 5-HT1A receptor and antagonists for 5-HT2A receptor are separately useful in the treatment of neuropsychiatric diseases, but no drugs having agonist activity for 5-HT1A receptor together with antagonist activity for 5-HT2A receptor in a selective and potent manner have been reported.    [Non Patent Literature 1] D. P. Taylor, Neuropeptides. 19 Suppl: 15-19 1991    [Non Patent Literature 2] P. Seeman, Can. J. Psychiatry. 47: 27-38, 2002    [Non Patent Literature 3] C. J. Schmidt, Life Science. 56 (25): 2209-2222, 1995